Safety release for blasting shells



SAFETY RELEASE FOR BLASTING SHELLS Filed March 15, 194

INVENTOR QTTORNEY Patented Mar. 28, 1950 SAFETY RELEASE FOR BLASTING SHELLS Hilding V. Williamson, Chicago, Ill., assignor to Cardox Corporation, Chicago, Ill., a corporation of Illinois Application March 15, 1946, Serial No. 654,626

21 Claims. 1

This invention relates to blasting cartridges or shells and more particularly to the provision of asafety pressure release means for such cartridges or shells.

The blasting cartridges with which the invention is concerned are of the type disclosed in Patent 2,207,191, issued to Eric Geertz on July 9, 1940. One use of these blasting cartridges is to break down material, such as coal which is being mined. Another use is to fracture slag which is formed in open-hearth furnaces, as is disclosed and claimed in Patent 2,151,264 to William C. Cavanagh, dated March 21, 1939.

These blasting cartridges in general consist of a thick walled body having a chamber in which liquid carbon dioxide is confined under high pressure. Located within the carbon dioxide chamber is a chemical heater unit for the generation of heat to convert the liquid carbon dioxide to vapor and greatly increase its pressure. The chemical heater unit is generally ignited by an electric match having circuit connections to the exterior of the cartridge. At one end of the cartridge'is a replaceable wall section constituting a shear plate which ruptures'when the pressure of the carbon dioxide vapor has reached a predetermined high value. This sudden rupture of the shear plate releases the confined pressure so that a material breaking eifectis obtained.

Due to faulty operation of the cartridges in some instances, which may result from too small a charge of carbon dioxide or an imperfect chemical heater unit, they do not generate suflicient pressure to rupture their shear plates. When this occurs, it is necessary that the defective cartridge be removed from its drill-hole so that an:- other can be substituted and so that the defective cartridge may be reconditioned for use. This handling of defective cartridges, however, is dangerous because the shearing action may be delayed and the shear plate may rupture while the cartridge is in the hands of or near an operator.

It is an object of the present invention to provide means in these blasting cartridges which will result in the gradual escape of the carbon dioxide vapor after the cartridge has been fired, to take care of a possible failure of the shear plate to rupture.

A further object of the invention is to provide a. safety pressure release of this character which will not alter the construction or normal operation of the cartridges now being employed.

A further object of the invention is to provide a safety pressure release which will be very inexbe referred to.

pensive and consequently may be applied to every cartridge without materially increasing its cost.

A preferred embodiment of this invention is illustrated in the accompanying drawings in which:

Figure 1 is a longitudinal sectional view through the axis of a blasting cartridge to which the invention has been applied, and

Figure 2 is a-plan view of the shear plate used with the invention.

The invention contemplates the provision of two general types of pressure safety release means, both of which have as their common purpose to cause a slow escape of carbon dioxide from a cartridge after it has been fired, so that the pressure will be bled off although the shear plate does not rupture. The first type of safety pressure release means serves to initiate the escape of pressure after the pressure has reached a relatively low value and this escape of pressure will continue while the pressure continues to build up to the high value required to rupture the shear plate. This action is not dependent upon an increase in temperature of the cartridge.

The second type of pressure release means with which the invention is concerned, functions to release the pressure as a result of a substantial rise in the temperature of the cartridge. This takes advantage of the fact that any cartridge which has been fired becomes heated due to the burning of the chemical heater unit. If insufficient pressure'is developed in the cartridge to rupture the shear plate. suflicient heat nevertheless will be generated to elevate the temperature of the cartridge. This elevated temperature serves to Weaken the safety release means of this second type contemplated by the invention. so that it will rupture or blow out and result in the escape of the pressure which is developed. This second type of safety pressure release means, preferably, has approximately the same rupturing strength under cold conditions as the main shear plate so that if the cartridge is a normal one and the shear plate ruptures, there will be no prior escape of gas due to rupture of the safety release means.

For a complete descriptionof the entire cartridge, the aforementioned Patent 2,207,191 may The accompanying drawings show only the discharge end of such a cartridge. In this drawing, the main body of the cartridge is indicated at 5 and this provides the chamber 6 to contain the liquid carbon dioxide, the chemical heater unit and the electrical match. An

orifice l is at the discharge end of the body 5 and within this opening is formed a recessed shoulder 8. outwardly from the shoulder 8 are internal screw threads 9. Screwed into the threads 9 is a discharged cap 10 which is hollow but which has discharge ports l2 through the wall thereof. These discharge ports [2 preferably incline outwardly and rearwardly toward the main body in so that the escaping 3 carbon dioxide vapor will be directed rearwardly and will tend to advance the cartridge into the drillhole in which it is located. Notches l3 are formed in the cap H) to enable ;;it tube-gripped by a wrench in assembling and disassembling this cap relative to the mainfbody 5.

The cap it serves to hold -inpla'ce against "the shoulder 8 a wall section made up of a shear plate 14 and a pressure releasecdisc. I15. sThe disc I 5 lies against the plate id in a face=to-face relationship and the disc I 5 is located an the at." The liquid carbon-dioxide which is under its charging pressure-within "the as; body 5 cannot, h'oweven e'scape' through these openings lfi'because' of the location-of the-disc 15 on'the inner side-of the plate I 4. "It' is, therefore-appa'rentthat theWallf-section inade up of the main shear plate l 4 f and the safety pressure release disc 15 have'th'eir combined thickness reduced at very small isolated ar'e'as" to-'-'provide portions of reduced rupture strengthrelativeto the com-' bined rupture strength of these two members.

It has been pointed out that one type of safety release meahscontemplated byth invention results in the initiation of thefbleeding down of the carbon dioxide-{vapor after its: pressure. has reached a-relatively low value. For example, itmay be desired that thisfcarbpn dioxidefva'por eginito ape a t r i -hes'.rsached f r sur of 0 lb n u r inche it i now t a the pressure. will always rise tofthis value if the chemical heater unit' is ignited everi though it, may not rise torthe .higher lpressure .which is necessary to rupture the main lshearplate Hi. If this-type saet nrs ur sl ase fs d r the disc- 15 may, v be made of the sar e grnaterial of which the shear plate, IA is made and this generally will be steel/ although it is -=possible to employ copper and other relatively strong metals for this purpose.

The safety ,disc 1 should ,be of- ;such a thi ness relative to the-shear strength of" this ma-. terial that it will* rupture {at the openings i6 when the internal pressure is-reached at which it is desired that the initiation of the vapor bleed-oh" will occur. Forexample, the thickness of this material may be such that it will rupture at the openings lBQata pressure of 5,000,pounds per square inch and this will occur either upon the sudden generation of this pressure, or upon the gradual attainment of this pressure.

It is referable that the openings HS-be of very ..found that these openings may advantageously be one-sixteenth inch in diameter and may be lfoury-imnumber. '.It.is preferable that there be more than onesuch opening I6 because if only one were present,, it might become obstructed.

With afhole one-sixteenth inch in diameter and using 'a steel disc having a shear strength ;.of 3&,GlOO :lbs. per square inch, a disc thickness 0f .QQ2-inch will result in the rupture of this disc at the openings it at a pressure of about 5,000 lbs. per square inch. If sheet copper having a shear strengthof 'lQ QQQ IbS. per square inch is used, and the holes It are of one-sixteenth inch diameter, a disc thickness of .OGiinch will result in itsrupture at 5,000 lbs. per square inch internal pressure.

If the pressure continues to rise within chamher 6 to the necessaryhigh value, both the shear plate 44 and the safety disc lfi will shear at the opening 7. As has been noted, openings .1 6 should be so small that they will not prevent the .attainment of this-high pressure.

"If it is desired to employ the second. type of safety pressure release, ,set forth above, the disc i5 is rnerelymade of a diiferenhmaterial. This material should be one Whichhas a reduced sheaLrstrengthupon heatilldor it may be one which, when heated, gradually flows and yields upon exposure to agproiongedpressure. Suitable materials for thispurpose are lead and a rolledflead-antimony alloy consisting of lead with up to five percent antimony. The thickness of thismfa-terial of which thedisc liiis made should be such" that it will have .a rupture strength at the relatively small openings it which is approximately equal to the combined rupture strength of the disc J5 and plate .lgl at the relatively large opening 1. If this pressure is 15,000 lbs. per square inch, and if the .mainshear plate l l h as holes l6 therethrough which are ofonesixteenth inch diameter, a lead disc it may be employed which is one-thirtyesecond inch thick. If a pressureis suddenly applied to the interior of the main body 5, ,as would occur with a normal cartridge, this ,lead disc would shear at the openings ataboutrliOOO lbs. per square inch and thisis approximatelythe pressure at which both the mainshear plate-lg? and disc shears at the opening I. w

If the internal'pressure does not rise to asufiicientlyhigh value to rupture both the safetydisc liand the main shear plate M, .the temperature of the cartridge will nevertheless rise and at a temperature of. F. the safety pressure release disc flii of thislead material will rupture at about 5,500 lbs. per square inch. Or, if the temperature should rise to 212 F., this lead disc will rupture at. about 2,7 00.lbs.. per square inch.

If the safety dis 15 is made of a relatively soft material aslead, it will serve as a gasket on the shoulder, 8 to'prevent the escape of carbon dioxide. If a hard material as steel is used for the disc L5, it will bernecessa y .to employ a gasket between thedisc l5 andshoulderfi.

This second type .of safety pressure release means has the advantage over the first type discussed above in that there will be no loss of internal pressure due to rupturing of the safety disc I5, inasmuch as with a normal cartridge the lead or like soft material disc will not rupture until approximately the rupture strength of the main shear plate.

The first type of safety pressure release which occurs in any event upon attainment of a relatively low pressure irrespective of the rise in temperature of the cartridge, nevertheless has the advantage that it is positive and rapid in its operation.

With both types of safety pressure release means, a cartridge which has been fired but which does not.discharge in the normal manner, may be handled with complete safety as its pressure will have been bled oil. There will consequently be no danger of the partridge suddenly discharging when it is being handled. The defective cartridge can then be reconditioned and be put back in use.

Having thus described the invention, I claim:

1. A blasting cartridge comprising a hollow body adapted to receive a charge of liquid carbon dioxide and a chemical heater unit that is burned to effect vaporization of said liquid charge and to raise its pressure to the value at which it is to be released to perform its intended work, said body having a discharge orifice through which the vaporized charge is released, a pair of members lying against each other in sealing relation with said orifice having a combined overall rupture strength which will cause both members to shear out of the orifice simultaneously upon the attainment of the intended work performing pressure in the hollow body, the outer one of said members supporting the inner member against the pressure in the hollow body and having a relatively small area of reduced support to provide a portion of reduced rupture strength relative to the combined rupture strength of said members, and means retaining said members in sea1ing relation with said orifice.

2. A blasting cartridge comprising a hollow body adapted to receive a charge of liquid carbon dioxide and a chemical heater unit that is burned to effect vaporization of said liquid charge and to raise its pressure to the value at which it is to be released to perform its intended work, said body having a discharge orifice through which the vaporized charge is released, a pair of members lying against each other in sealing relation with said orifice having a combined overall rupture strength which will cause both members to shear out of the orifice simultaneously upon the attainment of the intended work performing pressure in the hollow body, the outer one of said members having an opening of relatively small.

area to provide a portion of reduced rupture strength relative to the combined rupture strength of said members when said members are subjected to an elevated temperature for a prolonged period of time, and means retaining said members in sea1ing relation with said orifice.

3. A blasting cartridge comprising a hollow body adapted to receive a charge of liquid carbon dioxide and a chemical heater unit that is burned to effect vaporization of said liquid charge and to raise its pressure to the value at which it is to be released to perform its intended work, said body having a discharge orifice through which the vaporized charge is released, a pair of members lying against each other in sealing relation with said orifice having a combined overall rupture strength which will cause both members to shear out of the orifice simultaneously upon the attainment of the intended work performing pressure in the hollow body, the outer one of said members having an opening therethrough of relatively small area to provide a portion of reduced rupture strength relative to the combined rupture strength of said members, and means retaining said members in sealing relation with said orifice.

4. A blasting cartridge comprising a hollow cylindrical body adapted to receive a charge of liquid carbon dioxide and a chemical heater unit that is burned to efiect vaporization of said liquid charge and to raise its pressure to the value at which it is to be released to perform its intended work, said body having a discharge orifice at one end through which the vaporized charge is released, and providing a shoulder around said orifice, a pair of members lying against each other in sealing relation with said shoulder having a combined overall rupture strength which will cause both members to shear out of the orifice simultaneously upon the attainment of the intended work performing pressure in the hollow body, the outer member having an opening of relatively small area, and the rupture strength of the inner member at said opening being less than the combined rupture strength of said members when said members are subjected to an elevated temperature for a prolonged period of time, and means retaining said members in sealing relation with said shoulder.

5. A blasting cartridge comprising a hollow cylindrical body adapted to receive a charge of liquid carbon dioxide and a chemical heater unit that is burned to effect vaporization of said liquid charge and to raise its pressure to the value at which it is to be released to perform its intended work, said body having a discharge orifice at one of its end portions through which the vaporized charge is released and providing a shoulder around said orifice, a pair of members lying against each other in sealing relation with said shoulder having a combined overall rupture strength which will cause both members to shear out of the orifice simultaneously upon the attainment of the intended work performing pressure in the hollow body, the outer member having an opening of relatively small area, and the rupture strength of the inner member at said opening being less than the combined rupture strength of said members when said members are subjected to an elevated temperature for a prolonged period of time, and means having a threaded engagement with the body and urging the members toward the shoulder to hold the inner member in sealing relation with said shoulder.

6. A blasting cartridge comprising a hollow cylindrical body adapted to receive a charge of liquid carbon dioxide and a chemical heater unit that is burned to effect vaporization of said liquid charge and to raise its pressure to the value at which it is to be released to perform its intended work, said body having a discharge orifice at one of its end portions through which the vaporized charge is released and providing a shoulder around said orifice, a pair of members lying against each other in sealing relation with said shoulder having a combined overall rupture strength which will ause both members to shear out of the orifice simultaneously upon the attainment of the intended work performing pres- I asoaiee:

surein; thehol-low body,

ru ture stren thv of: the inner member at said opening being-r less: than: the" combined rupture strength)oi.isaid;;members, and means. engaging said body and the; peripherall portion of the outer-' member and. urging; the members toward the shoulder to hold the-inner member insealing relation with said shoulder;

'7. A blasting cartridge comprising a hollow body adapteditcx receiveracharge of liquid carbon, dioxide-and a chemical heater unit that is burned rte-effect vaporization of said liquid charge and: toiraise its :pressure to, the value at which it isto :be released 'tmperformaits. intended work,

said body having, discharge orifice. throu h. which -,the, -vaporizedcharge vie-released,- a pair of members of: larger size than said orifice lying against each other; in sealing relation with said 8. A blasting cartridgecomprising; a hollowbody adapted to receive a charge of liquid carrbon dioxide and a chemical-heater unit that is burned to efiect vaporization of said liquid char er and to raise its press-uretothevalue at which it is -to-bereleased to perform its intended work, said body having a discharge orifice through which'the vaporizedcharge isreleased, a-pair: of

members lying a ainst each-other and of larger-- sizethan saidorifice, means retaining said members over said orifioein sealingrrelationtherewith, the inner one of said members being of;lessstructural-strength than-the outermember, and the combined thickness of said members being reduced at a materially'smal'l area-to provide a portion of reduced rupture strengthre'lative to the combined rupture strength of said members.

9. A blasting cartridge comprising a hollow-- bodyadapted to receive a charge ofvliouidwcar bondioxide-and a chemical heater unit that is burned to effect vaporization ofsaid liquid charge'and to-raise its pressure to; thevalue at:

which: it is to be released toperform its in.- tended work, said body having a discharge-orifice through which the vaporized charge is: released, a pair of members ofra larger size than saidorifice lying against-each other in sealing relation with said orifice having a combined overall rupthe outer m'emberzhava. ing; an .7 Opening-oi relatively small area, and the:

turestrength which will causerboth members toshear out of the orifice simultaneously upon the attainment of the intended workperforming pressure'in the hollow body, thezinnerone offsaid' members being thinnerthan the outer member;.

and'the outer oneof' said members: having an opening ofrelatively small area to provide a-.por tiono-f" reduced rupture strength relative to thecombined rupture strength of'tsaidmembers, and meansretaining said'memberszin sealing relation with said orifice;

10. A blasting cartridge comprising a hollow cylindrical body adapted to receiveza charge of liquid carbon dioxide and, a chemical heater unit.

thatisburnedto effect-vaporization ofsaid liquidi charge and to raise itspressureto the value atwhich; itisz. to: be; released to;.perform its in.-

tended work, said body having a discharge orifice at one of its end portions through whichthevaporized charge is released and providing a shoulder around said orifice, a relatively thin member seated on said shoulder to close said orifice, and a relatively thickmemb'er overlying said thin member, said members havinga'combined overall rupture strength which will cause both members to shear out of the orifice simultaneously upon the attainment of'the. intended work performing pressure inthe hollow body, theouter thick member having an opening of relatively small area to provide a portion of reduced rupture strength relative tothe combined rupture strength of said members when said members are subjected to an elevated temperature for a prolonged'period of time, and'restraining means engaging said body in the peripheral portionof the thick member to urge the thick member toward the shou der and thereby hold the thin member in sealing relation with-said shoulder.

11. A blasting cartridge comprising a hollow cylindrical body adapted to receive a charge of liquid carbon dioxide and a chemical heater unit that is burned to effect vaporization of said liquid charge and to raise its pressure tothe value at which it is to be released=to perform-its intended work, saidbody having a discharge orificeat one of its end portions through which the vaporized charge is released and providing a shoulder around said orifice, a relatively thin member seated on said shoulder to close said orifice, and a relatively thick member overlying said thin member, said members having a combined overall rupture strength which will cause both members to shear out of 'the orifice simultaneously upon the attainment of the intended" Work performing pressure in the hollow body, the outer thick member having a plurality of spaced openings, each of relatively small area, to provide portions of reduced rupture strength relative to the combined rupture strength of said members, and restraining means'engaging said body and the peripheral portion to urge the thick member toward the shoulder and thereby hold the thin member insealing relation with said shoulder;

12; A blasting cartridge comprising a hollow body adapted to receive a charge of liquid carbon dioxide and a chemical heater unit that is burned to effect vaporization of said liquid charge and to raise its pressure to the value at which it is tobe released to perform its intended work, said body having a discharge orifice through which the vaporized charge is released, a plate disposed across said orifice having an opening of relatively small area, a disc on the interior side of the plate and of substantially the same peripheral shape as the plate, the rupture strength of said disc at the plate opening being less than the combined rupture strength of the plate and disc, said disk and said plate-having a combined overallrupture strength which will cause both members to shear out of the orifice simultaner ously upon the attainment of the intended work performing pressure in the hollow body, and. means for retaining the plate and the disk in, sealing engagement with the body at said orificeto prevent leakage.

13. A blasting cartridge comprising a hollow body adapted'to-receive a charge of liquid carbon dioxide and a chemical heater unitthat is burnedto eiiect vaporization of said liquid charge and toraise its pressure to thevalue at which it is; to be released to perform its intended work, said body having a discharge orifice through which the vaporized charge is released and presenting a shoulder around said opening, a disc seated on said shoulder, a plate bearing against said disc, said plate having an opening normally closed by said disc, the rupture strength of said disc at said opening being less than the combined rupture strength of the plate and disc when they are subjected to an elevated temperature for a prolonged period of time, said plate and said disk having a combined overall rupture strength which will cause both members to shear out of the orifice simultaneously upon the attainment of the intended work performing pressure in the hollow body, and means engaging said body and the periphery of said plate to urge the plate toward the shoulder and thereby hold the disk in sealing relation to the shoulder.

14. A blasting cartridge comprising an elongated hollow cylindrical body adapted to receive a charge of liquid carbon dioxide and a chemical heater unit that is burned to effect vaporization of said liquid charge and to raise its pressure to the value at which it is to be released to perform its intended work, said body having one of its end portions open to provide a discharge orifice through which the vaporized charge is released, a plate disposed across said orifice, retaining means having a threaded engagement with the body and urging said plateagainst the body at its open end, and a disc between said open end of the body and said plate and held in sealing relation with the body by said plate and said retaining means, said plate having an opening and the rupture strength of the disc at said opening being less than the combined rupture strength of the plate and disc, said plate and said disk having a combined overall rupture strength which will cause both members to shear out of the orifice simultaneously upon the attainment of the intended work performing pressure in the hollow body.

15. In a blasting cartridge, the combination with a hollow body adapted to receive a charge of liquid carbon dioxide and a chemical heater unit that is burned to effect vaporization of said liquid charge and to raise its pressure to the value at which it is to be released to perform its intended work, said body having a discharge orifice through which the vaporized charge is released, of means for closing said orifice, said orifice closing means comprising two members having a combined overall rupture strength which will cause both members to shear out of the orifice simultaneously upon the attainment of the intended work performing pressure in the hollow body, the outer one of said members supporting the inner member against the pressure in the hollow body and having a very restricted area of reduced support to provide a rupture strength substantially less than said combined overall rupture strength which will cause shearing to occur at said restricted area only to slowly bleed off the vaporized charge at a pressure below the intended work performing pressure.

16. In a blasting cartridge, the combination with a hollow body adapted to receive a charge of liquid carbon dioxide and a chemical heater unit that is burned to effect vaporization of said liquid charge and to raise its pressure to the value at whichit is to be released to perform its intended work, said body having a discharge orifice through which the vaporized charge is released, of means for closing said orifice, said orifice closing means comprising two members having a combined overall rupture strength which will cause both members to shear out of the orifice simultaneously upon the attainment of the intended work performing pressure in the hollow body, the outer one of said members supporting the inner member against the pressure in the hollow body and having a very restricted area of reduced support to provide a rupture strength substantially less than said combined overall rupture strength, when said members are subjected to an elevated temperature fora prolonged period, so that shearing will occur at said restricted area to slowly bleed off the vaporized charge if the intended work performing pressure is not developed.

17. In a blasting cartridge, the combination with a hollow body adapted to receive a charge of liquid carbon dioxide and a chemical heater unit that is burned to effect vaporization of said liquid charge and to raise its pressure to the value at which it is to be released to perform its intended work, said body having a discharge orifice through which the vaporized charge is released, of means for closing said orifice, said orifice closing means comprising two members of the same diameter and having a combined overall rupture strength which will cause both members to shear out of the orifice simultaneously upon the attainment of the intended work performing pressure in the hollow body, the outer one of said members supporting the inner member against the pressure in the hollow body and having a very restricted area of reduced support to provide a rupture strength substantially less than said combined overall rupture strength which will cause shearing to occur at said restricted area only to slowly bleed off the vaporized charge at a pressure below the intended work performing pressure.

18. In a blasting cartridge, the combination with a hollow body adapted to receive a charge of liquid carbon dioxide and a chemical heater unit that is burned to effect vaporization of said liquid charge and to raise its pressure to the value at which it is to be released to perform its intended work, said body having a discharge orifice through which the vaporized charge is released, of means for closing said orifice, said orifice closing means comprising two members of the same diameter and having a combined overall rupture strength which will cause both members to shear out of the orifice simultaneously upon the attainment of the intented work performing pressure in the hollow body, the outer one of said members supporting the inner member against the pressure in the hollow body and having a very restricted area of reduced support to provide a rupture strength substantially less than said combined overall rupture strength, when said members are subjected to an elevated temperature for a prolonged period, so that shearing will occur at said restricted area to slowly bleed off the vaporized charge if the intended work performing pressure is not developed.

19. A blasting cartridge, comprising a hollow body adapted to receive a charge of liquid carbon dioxide and a chemical heater unit that is burned to effect vaporization of said liquid charge and to raise its pressure to the value at which it is to be released to perform its intended work, said body having a discharge orifice through which the vaporized charge is released, and means for closing said orifice, said orifice closing means comprising two members having a combined overall rupture strength which will cause both memberato shea-rout of the"oriflce simultaneously' upon the attainment of the intended'work performingpressure in thehollow body, the-outer one-or said membershaving 'an opening of-relati-vely small area, the innermember-being of less 1 structural-strength than the outer'member so that it "will-shear atthe opening in said" outer member to release the vaporized charge-when said vaporized chargedoes not attainits intended work performing pressure.

'20. A blasting cartridge, comprising'a hollow bodyadapted to receive a. charge ofliquid carbon dioxideand a chemical heater unit that isburned toeffect vaporization of said'liquid charge and to raise its pressure to the valueat which-it 'is -to-be released to perform its intendedwork, said body having a discharge-orifice throughwhi'ch the charge is released, andmeans for closingsaid orifice, said orifice closing meanscomprisin'g two 'disk shaped members having a-combined overall rupture strength which will-cause both members to shear out of the orifice simultaneously "upon the attainment of the intended wo'rkperforming pressure in the hollow body, the outerone of said members being'of greater thickness relative to the inner member and having a-plu-rality-of spaced openingsof relatively small area; theinner member being of less structural strength than the outer member so that it Will shear-at the openings in said outer -memb'er to' release the vaporized charge when said vaporized charge-does not attain its intended-workperforming pressure.

1 21. In "a device-ofrtheitypedescribed, a fluid charge containing "body havinga discharge. orifice, a "disk shaped "metal member closing the dischargeorificebf said body,'a:perf0rated plate located 'outwardly-of'said disk=shaped. member, means maintaining said plate' and said disk *in sealing-relation with the 'discharge orifice, said plate and diskbeing adapted to shearsimultane- 'ous'ly'at the discharge orifice upon the attainmentof a predetermined pressure in the charge containing body, and said disk being adapted. to shear at the-perforations of said plate at a pressure below the predetermined pressure.

HILDING V. WILLIAMSON.

REFERENCES 5 CITED "The following referenceseare-of record in .the file. of this patent:

' UNITED STATES: PATENTS Number Name Date 138,171 Matthews Apr. 22,1873 1,250,680 Sheldon Dec. 18, 1917 1,805,541 Ferrell et al May 19, 1931 2,207,191 Geertz Ju1y'9, 1940 2,242,547 Raymond May'20, 1941 2,326,771 Eidson -1 Aug. 17, 1943 FOREIGN PATENTS Number Country Date 276,279 Great Britain 1927 

